Conventional passenger aircraft used in commercial aviation typically include passenger windows mounted along the sides of the aircraft fuselage. The laterally-facing windows are typically arranged in a single row in a window belt that extends between the forward and aft ends on each side of the fuselage. Each window is typically mounted in a window cutout formed in the sides.
During service, the aircraft is subjected to a variety of different loads of different magnitude and orientation. For example, during flight, the weight of the aircraft and the aircraft payload (e.g., passengers, baggage, cargo) are supported by the aircraft wings. During normal cruise flight, the weight of the aircraft and payload cause a bending moment on the fuselage. The bending moment generates an in-plane shear load on each side of the fuselage. The shear load results in tension and compression components of the shear load in the side region and which are oriented at approximately 45 degrees relative to the aircraft longitudinal axis. The shear load passes through the window belt connecting the crown region of the fuselage to the keel region of the fuselage.
Conventional aircraft windows typically have an oval shape and are spaced along the aircraft fuselage at a relatively short pitch distance. The pitch distance between the windows typically corresponds to the distance between the circumferential frames which are typically spaced at approximately 22-24 inches along the interior side of the fuselage skin. The combination of the relatively short pitch distance and the oval shape of conventional aircraft windows results in a discontinuous or contorted load path for the shear loads. In this regard, the oval-shaped windows and the pitch distance prevent the shear load from passing in a straight line between the windows and instead create a discontinuity in the shear load path forcing the shear load to go around each oval-shaped window.
The discontinuous load path results in stress concentrations along the edges of the window cutouts requiring an increase in skin thickness around the cutouts to maintain the stress below the allowable limits of the skin material. The increased skin thickness increases the cost, complexity and production time of the aircraft. In addition, the increase in weight due to the increased skin thickness reduces the payload capacity of the aircraft and increases fuel consumption.
As can be seen, there exists a need in the art for a window cutout having an optimized shape that improves the load path between the window cutouts in the side regions of the fuselage. In addition, there exists a need in the art for an arrangement that optimizes the skin thickness in areas adjacent to the window cutouts.